Fill level monitoring systems for flow measuring devices are known. For instance, a measured substance monitoring electrode (MSM electrode) in the case of horizontal installation is arranged with reference to the cross section of the measuring tube at the uppermost point thereof. By determining the electrical resistance or the conductivity between the MSM electrode and the medium, derived e.g. via a reference electrode or a metal process connection in contact with the metal housing of the flow measuring device, the contact between MSM electrode and medium and, thus, the complete filling of the tube is monitored. In such case, the medium has compared with air always a higher conductivity. If the conductivity sinks below a predetermined limit, then a partial filling is detected. The limit is dependent on, among other things, the specific conductivity of the medium, the nominal diameter, the size and position of the MSM electrode as well as the properties of the measuring tube lining. Therefore, depending on application, a calibration is required for determining the limit.
Moreover, temperature sensors are known, which are applied in flow measuring devices. Already known, for example, are German Patent, DE 10 2009 0046 653 A1, European Patent, EP 1 387 148 A2 and German Patent DE 10 2007 005 670 A1, in which temperature sensors are applied and utilized in measuring electrodes of an MID. These sensors serve, however, not for fill-level monitoring of a high degree of filling but, instead, only give a warning signal, when in the case of horizontal installation and horizontal connecting axis of the measuring electrodes, the degree of filling in the pipe sinks below 50%. This could be achieved, when the connecting axis of the measuring electrodes in the installation is vertically oriented. Disadvantageous, in such case, however, is the influencing of measuring performance by small gas bubbles in the medium, which flow along the inner upper side of the measuring tube.